code: def test_dissolve_dropna():
      gdf = geopandas.GeoDataFrame(
          {
              "a": [1, 1, None],
              "geometry": geopandas.array.from_wkt(
                  ["POINT (0 0)", "POINT (1 1)", "POINT (2 2)"]
              ),
          }
      )
  
      expected_with_na = geopandas.GeoDataFrame(
          {
              "a": [1.0, np.nan],
              "geometry": geopandas.array.from_wkt(
                  ["MULTIPOINT (0 0, 1 1)", "POINT (2 2)"]
              ),
          }
      ).set_index("a")
      expected_no_na = geopandas.GeoDataFrame(
          {
              "a": [1.0],
              "geometry": geopandas.array.from_wkt(
                  ["MULTIPOINT (0 0, 1 1)"]
              ),
          }
      ).set_index("a")
  
      assert_frame_equal(
          expected_with_na, gdf.dissolve("a", dropna=False)
      )
      assert_frame_equal(expected_no_na, gdf.dissolve("a"))
  
imports: import warnings
  import numpy
  import pandas
  import geopandas
  from geopandas import GeoDataFrame, read_file
  from pandas.testing import assert_frame_equal
  import pytest
  from geopandas._compat import PANDAS_GE_15, PANDAS_GE_20
  from geopandas.testing import assert_geodataframe_equal, geom_almost_equals
label_desc: Use image node_id 19 for calling a global function with example usage: test_dissolve_dropna() without return types